I agree that I used a lot assumptions in my calculation

You all know that tax calculation is not simple and I have to simplifed it to make my case, and here is my assumption

1) the $ amount I used in the calculation is assumed final taxable income (after all dedection  & is in line 15 in 1040)

2) As I asid: the tax bracket (28%) is my highest tax bracket, not my effective tax bracket. please note, tax bracket change every several years & you have to make some assumption.

3) I used $53K SS benefit in the calculaton.  $53000 Sn benefit is the one I assumed several years ago when I started plan my retirement.  

Better and detail calculation can be found here

https://www.calcxml.com/calculators/how-much-of-my-social-security-benefit-may-be-taxed?skn=#results   My key point is:   假如您每年需要从401K里拿出10万元, 那么您不仅要交这十万元的税; 您还会因为收入太高而需要补交原本不需要交的社会保险金的税。这两个税加在一起有可能比您现在的税率高很多。